1. Field of the Invention
The present invention relates to improvements to screw presses and more particularly to positive feed devices and removable screens for screw presses.
2. Description of the Prior Art
The screw press for separating liquids from solid matter has been widely used in a number of industries. The trend in the prior art appears to have been the development of specialized presses dedicated to particular materials. For example, our U.S. Pat. Nos. 4,279,197 and 4,266,473 are well suited to dejuicing grapes for the wine and juice industry. The '473 patent discloses a predrainer press for removing free run juice from grape must and utilizes the principle of a gradually tapered screw body which provides gentle pressing as the must moves from large volume flights to small volume flights. The '197 patent describes a final press utilizing a straight body screw and a large pressing chamber. The screw creates a pressure on the must in the chamber to thereby press out all of the usable juice, leaving a very dry residual cake. The present invention is concerned with the predrainer type of screw press and certain improvements that permit this type of press to be utilized in dewatering of a large variety of materials of varying consistencies and viscosities as well as fruits.
The following are typical problems encountered in using a predrainer type screw press with various types of materials:
1. Highly liquid material having low solid content.
When such material is introduced into the hopper, it is common for insufficient solids to accumulate in the screw flights to produce the desired pressure. The result is that excessively wet solids emerge from the press. In the past, it has been necessary to thicken such material by use of prestrainers, and other devices before pressing, adding to equipment and handling costs.
2. Heavy, spongy or viscous materials.
When these types of materials are fed into the inlet feed section of a predrainer press, there is a tendency for the solids to pack or stick to the screw body and thread faces. When this occurs, the mass of material turns with the screw and does not feed down the press. This action is termed "slippage." Incoming material then simply rests on the packed flights which slip past as the screw rotates.
3. Viscous material with too high a head in the inlet hopper.
Viscous material that would otherwise feed properly may slip when the height of the material in the hopper becomes excessive. The weight of the material then causes excessive packing and sticking of the material in the inlet flights of the feed screw producing slippage as discussed above.
4. Material fed under pressure.
Some types of material which are fed into a screw press under pressure may have a velocity sufficient to cause solids to stick to the feed screw which thereby results in slippage.
Therefore, a much needed improvement in predrainer type screw presses is a feed section and feed screw design that will permit a number of different highly liquid materials having a wide range of physical characteristics to be continuously fed to the press with positive feed of the material.
Another area needing improvement is that of the filter screens. Many materials tend to clog the filter screens which therefore require frequent cleaning of the screens. Our '197 patent discloses an important advance in this area. The screens are mounted on hinged frames which permit access to the inside surfaces by opening of the frames with a minimum disassembly of the machine. The disclosed design allows ease of cleaning but suffers from the problems of leakage around the edges of the frames. Thus, an improved edge seal is needed.